Corrosion is a problem associated with virtually all metal objects that are exposed to an oxidizing environment. The effects of corrosion are particularly noticeable in automobiles, ships, aircraft, heavy machinery and bridges. Corrosion is a serious problem in the road construction industry, in various industrial processes and in medical devices. Metal corrosion is especially severe in harsh environmental conditions, e.g. exposure to acid, base or salts. Corrosion resistant coatings such as zinc, epoxy, tar, polymer and paint are typically applied as adhesive coatings on the exposed surfaces of a metal object providing a barrier to environmental attack. Although such coatings can comprise simply a polymeric composition, they commonly includes corrosion inhibiting heavy metal or toxic organic compounds to enhance corrosion resistance. Other diverse corrosion inhibiting compositions and materials are disclosed in U.S. Pat. Nos. 5,152,929, 4,818,777, 5,098,938, 5,021,489 and 5,183,842.
The application of a corrosion inhibiting coating onto a metal object is, however, not a complete solution to corrosion because most coatings are subject to cracks, chips, or scratches which expose the bare metal to the corrosive environment. Even the existence of pinhole discontinuities in a coating can be defeat the anticorrosion function of a coating. In this regard, the effects of corrosion at discrete locations as a result of a chip or a scratch can be particularly severe because the effects of the corrosive elements are concentrated at the point of exposure. Accordingly, conventional corrosion inhibiting compositions are not completely satisfactory in providing corrosion resistance to metal objects.
Intrinsically conducting polymers (ICP), organic polymers that have poly-conjugated .pi.-electron systems, have been proposed as potential corrosion inhibiting compositions for metals. Such polymers have not heretofore been considered suitable as protective coatings because of the intractable nature of ICP's. That is, the class of ICP's lack the necessary properties, such as cohesion, adhesion, processability and stability, to be acceptable-for use as a protective coating on a metal object. Others have attempted to improve the properties of ICP's by modifying them or blending them with other polymers. For instance, U.S. Pat. No. 5,109,070 discloses sulfonated ICP; European Patent Application No. 0 497 514 discloses blends of ICP's and thermoplastic polymers; U.S. Pat. No. 5,160,457 discloses compositions of doped polyaniline and one or more thermoplastic, solution processable or thermoset polymers; and U.S. Pat. No. 4,983,690 discloses blends of polyaniline and a bismaleimide thermoset. Despite the widespread investigation of ICP's and ICP containing systems, viable corrosion protection systems employing ICP's remain an unfulfilled promise.